Circadian Regulation of Neuropeptides from the Hypothalamus.

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The central or master biological clock is found in the SCN, located in the hypothalamus. This clock operates at the molecular level through a combination of feedback loops, involving clock genes. At a basic level, hypothalamic nuclei outside the SCN express neuropeptides that are directly responsible for the control of energy balance, including neuropeptide Y (NPY) and proopiomelanocortin (POMC). While the SCN does indeed drive the coordination of overall circadian rhythms within the hypothalamus, we hypothesize that an endogenous cellular circadian system in these efferent neurons is required for the rhythmic expression of key neuropeptides and is essential for the control of energy balance. We also predict that the normal rhythmicity can be altered by nutrient excess and endocrine disrupting chemicals (EDC), classified as “obesogens”. We have used immortalized cell lines that express NPY/AgRP or POMC to demonstrate the circadian expression of these neuropeptides. We have also published that the saturated fatty acid palmitate can disrupt these rhythms, with omega-3 DHA rescuing the altered rhythms. Recently, my laboratory has found that the EDC bisphenol A (BPA) alters the expression of NPY and POMC. We will link changes to the intrinsic neuronal circadian machinery (including the rhythmic expression of clock genes Bmal1 and Per2) to hypothalamic neuropeptide gene expression using newly created hypothalamic cell lines from male and female Bmal1 knockout mice. We will also study how neuroinflammation, induced by palmitate and BPA, affects the normal circadian control of clock genes and neuropeptide expression and delineate the molecular mechanisms involved in this process. Aim 1: Understanding the molecular events involved in the palmitate-mediated disruption of rhythmic or circadian control of NPY/AgRP and POMC. We will define the role of the clock genes in the transcriptional regulation of these key genes using novle Bmal1 knockout cell lines and sophisticated molecular techniques, including siRNA knockdown and detailed promoter analysis. Aim 2: Characterizing the role of cellular neuroinflammation, caused by the saturated fatty acid palmitate or BPA, in the cyclical regulation of clock genes and hypothalamic neuropeptides. Changes in rhythmicity will be analyzed for mechanistic alterations at the levels of signal transduction pathways, epigenetic control, and the gene promoter. Although it is generally accepted that the body operates quite routinely on a classic day/night schedule, the molecular events involved in the circadian regulation of basic physiological processes are not yet understood. Since the intact circadian clock is critical for maintaining metabolic processes, including energy homeostasis in vivo, we now intend to define the hypothalamic neurons that play a role in this process, and ultimately to identify the underlying molecular mechanisms.